1. Field of the Invention
The present invention relates to a gas sensor for measuring a quantity of specific component in a measuring gas and a method of measuring thereof. More specifically, the present invention is directed to a gas sensor and a method capable of accurately and readily correcting a dispersion in output characteristics among sensors.
2. Description of Related Art
Hitherto, there is known a method of measuring a quantity of specific component such as oxygen gas, in which an electrochemical pump cell including a partition made of solid electrolyte such as a zirconia ceramic and provided with a pair of electrodes thereon is used, and the diffusion limiting current is measured when applying current between these electrodes. In the method, the diffusion limiting current varies with the difference in the structure of sensor element, particularly with the dispersion of the micro-structure of electrode and of the porosity in gas diffusion resistance layer. Accordingly, accurate measurement needs to apply a correction responding to the sensitivity of individual sensor elements.
Different from the sensors used in analyzers, there is a problem on correcting the dispersion among sensors as automobile parts. That is, dispersion among individual sensors in terms of sensor characteristic is not able to be adjusted from the interface side.
Consequently, sensors mounted on an automobile require any means to correct the dispersion among individual sensors.
For correcting that type of dispersion among the individual sensors, there are known methods such as:
1) a method, as shown in FIG. 8, in which a diffusion limiting current is divided into two routes using two resistors, 32 and 33, to adjust the diffusion limiting current to a predetermined value; and
2) a method in which after measuring the respective sensor characteristics, the measured characteristics are ranked, then as shown in FIG. 7, the fixed resistor 12 having a resistance value corresponding to each rank is built in the connector casing.
The method illustrated in FIG. 8 is configured by a circuit which comprises: an electrochemical pump cell 60 including a solid electrolyte partition 2, a pair of electrodes 3 and 4 formed on the inner surface and outer surface thereof, and a gas diffusion resistance layer 5 formed on the electrode 3; a power source 9; and a current detection means 10 both of which are arranged between output terminals 6 and 7 of the electrochemical pump cell 60, wherein a diffusion limiting current to be flowed to the electrochemical pump cell 60 is divided by the resistors 32 and 33, to thereby flow the current proportional to the concentration of the specific component in the measuring gas to the current detection means 10.
Further, according to a method shown in FIG. 7, a sensor is configured by a circuit which comprises: an electrochemical pump cell 60 including a solid electrolyte partition 2, a pair of electrodes 3 and 4 formed on the inner surface and outer surface thereof, and a gas diffusion resistance layer 5 formed on the electrode 3; a power source 9; and a current detection means 10 both of which are arranged between output terminals 6 and 7 of the electrochemical pump cell 60, wherein after measuring the characteristic thereof, the measured characteristic is ranked. Subsequently, as shown in FIG. 7, a connector casing in which a fixed resistor 12 corresponding to each rank is built and is combined with the electrochemical pump cell 60 to detect the current by a separate current detection means 15 which is connected to the fixed resistor 12 in series.
However, for a sensor having shunt resistors or a sensor having a fixed resistor responding to each rank, both of which are described above, they have disadvantages such that the number of terminals on the connector increases, the reliability decreases and the production cost increases.